Similar appearance of
childrenfrom the same
region of Asia due to a shared
gene pool

With the
exception of monozygotic twins, every one of
us is genetically different from every other human whoever lived. Each of us is
unique in terms of the combination of tens of thousands of genetically determined
characteristics that we possess. However, we clearly
have some traits in common with other people. Most of us have readily
identifiable male or female sexual characteristics which we share with
others of our gender. People who are closely related to each
other usually have even greater similarity
in appearance because much of their genetic makeup is
shared. Unrelated people
whose ancestors came from the same part of the world often are generally similar in terms of
such body features as skin and hair color, facial characteristics, body shape, and
stature. Not surprisingly, these traits have a strong genetic
component as well.
However, they can be affected by environmental influences. For instance, skin color
often can be darkened, or tanned, seasonally by prolonged exposure to ultraviolet radiation from the sun.
Likewise, stature can be affected by nutrition. When young children do
not receive sufficient calories in their diet, especially protein, their
growth is likely to be stunted--they will not reach their full
genetically programmed height.

Humans like to classify and
use identity labels for people and things with which we come in contact.
It satisfies our apparent need for a sense of order. In addition to
gender and age, most of us readily classify each other into
distinct categories on the basis of what we consider to be
races. In North America, people usually think in terms of
Black, White, Asian, Hispanic or Latino, and Indian or
Native American. These are all
archaic concepts of physical types that have little biological reality.Academics may use more
sophisticated sounding terms for these perceived biological groupings, such as Negroid , Caucasoid or Caucasian , and Mongoloid . Nevertheless, they
are still bad science. However,
they are important to contemporary life in North America because they reflectculturally defined
differences in our society.
They
are essentiallylabelsof ethnicity
that are used for categorizing and discriminating.

We now know that clearly distinct human
biological races do not now exist.
This does not
mean that our species is lacking anatomical and physiological variation
between populations. Rather, the true nature
of that variation is far more complex. It does not
correspond to commonly believed simple racial lines.

The physical
traits that we think of as clustering together among particular peoples often have much
broader distributions. They continue well outside of the geographic areas in which a
"race" is stereotypically supposed to exist. For instance, dark brown skin
is usually thought of as the key trait in distinguishing
sub-Saharan Africans from people
elsewhere in the world. However, dark
brown skin is also found in parts of southern Asia, Australia, New Guinea and on
the nearby
islands of Melanesia.

(Data for native populations collected by R. Biasutti
prior to 1940.)

Papua New Guinean(from the Southwest
Pacific Ocean)

The
non-African peoples with dark brown skin color (like the man in the photo
from New Guinea) do not share a close common ancestry with
Africans. Their skin coloration is largely due to natural selection rather than recent shared
descent. The environmental factors that led to dark brown skin among Africans
apparently led to
it elsewhere as well.

Genetically inherited traits
often have a clinal distribution. That is to say there
is a continuous, progressive gradation moving
from one geographic region to another. The
frequency of yellow-brown hair among
Australian Aborigines illustrates this trend (as shown by the map
on the left below). This
trait generally becomes more common with distance from the coast. Such patterns can
result when selective pressures differ from one region to another
and when people mate mostly with their immediate neighbors.Selective pressures favoring or discriminating against a trait may come from several sources. There may be
natural selection resulting from environmental constraints. At the
same time, there also may be patterns of culturally defined discriminatory
mate selection that vary from region to region.

Clinal distribution of hair
color among Australian Aborigines

Discontinuous distribution
of red hair in Britain

Sometimes, the
distribution of genetically inherited traits does not follow a pattern of gradual change
from one geographic region to another, but has a discontinuous distribution.
The frequency of red hair in Britain illustrates this sort of pattern. Note in the
map on the right above that there are several relatively isolated pockets where there is a high
frequency of people with red hair. Such a pattern can result when
groups of people migrate into a new area or when there are closed breeding
groups that
select mates based on such a trait.